In the semiconductor device such as a power module and a LED, it has a structure in which the semiconductor element is bonded onto a circuit layer composed of a conductive material.
For example, since a power semiconductor device of high-power control that is used to control wind power and electric vehicles such as electric automobiles generates a large amount of heat, as a substrate for mounting the power semiconductor device, for example, a ceramic circuit substrate in which a metal plate having an excellent conductivity and used as a circuit layer is bonded on a ceramic substrate composed of, for example, AlN (aluminum nitride) has been widely used conventionally.
For example, in the power module shown in Patent Document 1, it has a structure comprising a ceramic circuit substrate, one surface of which a circuit layer composed of metal is formed, and a semiconductor element bonded on the circuit layer. A heat sink is bonded to the other side of the ceramic circuit substrate, and the power module is configured so that the heat generated by the semiconductor device is transmitted to the ceramic circuit substrate side and dissipates to the outside via the heat radiation plate.
Here, when the electronic components such as semiconductor devices are bonded on the circuit layer, for example, as shown in Patent Document 1, a method using a solder material is widely used. Recently, from the viewpoint of environmental protection, for example, a lead-free solder which is Sn—Ag-based, Sn—In-based, Sn—Ag—Cu-based, or the like, is mainly used.
However, when, as described in Patent Document 1, when the electronic components such as semiconductor devices and the circuit layer are bonded together via the solder material, part of the solder is melted when used in a high temperature environment, and there is a possibility that bonding reliability between the circuit layer and the electronic components such as semiconductor devices is reduced.
In particular, in recent years, practical use of the compound semiconductor elements such as SiC or GaN is expected from silicon semiconductor, the improvement in heat resistance of the semiconductor element itself is expected, and therefore, it becomes difficult to meet the expectation by the structure which is bonded using the solder material as in the conventional one.
Therefore, as an alternative to solder, for example, in Patent Document 2, a technique in which a semiconductor element is bonded using a metal paste having metal particles and an organic substance has been proposed.
Further, in Patent Documents 3 and 4, a technique in which circuit electronic components such as semiconductor elements are bonded on a circuit using an oxide paste containing a reducing agent including metal oxide particles and an organic substance has been proposed.
In the metal paste that is described in Patent Document 2, it contains metal particles and an organic substance, and since the metal particles are sintered, the bonding layer consisting of a conductive sintered body is formed, and the electronic components such as semiconductor elements are bonded on the circuit layer via the bonding layer.
In the metal paste that is described in Patent Documents 3 and 4, a bonding layer consisting of a conductive sintered body is formed by sintering of metal particles produced by reducing metal oxide particles using the reducing agent, and the electronic components such as semiconductor elements are bonded on the circuit layer via the bonding layer.
Thus, when the bonding layer is formed of the sintered body of metal particles, the bonding layer can be formed at a relatively low temperature condition and the melting point of the bonding layer itself is increased. Therefore, the bonding strength does not significantly decrease even in a high temperature environment.